A wide array of resealable containers are known. Typically, a container such as in the form of a flexible bag or rigid walled housing, is provided with an opening that serves to provide access to the interior of the container. A lid or cover is positioned over the opening and bonded to the container, typically by heat sealing, to enclose and seal the container interior and its contents from the external environment. For bag type containers, a portion of the flexible wall of the bag may serve as the cover and be folded or otherwise positioned over an opening in the bag. A reseal feature enables the lid or cover, or a portion thereof, to be removed or otherwise repositioned so as to allow access to the interior of the container. After accessing the interior of the container, the lid or cover can be appropriately positioned over the opening and engaged with the container to thereby reseal the container.
Numerous strategies have been devised for the lid or cover to overlay a container opening and engage the container to thereby seal the interior of the container from the outside environment. An example of a sealing strategy is the provision of corresponding, e.g. male and female, engagement structures on the respective contacting surfaces of the container and lid. Another example is the use of a layer of a pressure sensitive adhesive on the contacting surfaces of the lid or cover, and/or the corresponding region of the container extending about the periphery of the opening. This latter strategy is widely used, particularly for disposable packaging as used for storing and preserving perishable items such as food in which it is desirable to minimize exposure to air. For example, U.S. Pat. No. 3,329,331 describes a box having a top or wall section resealable by use of a layer of pressure sensitive adhesive.
As packaging technology developed, polymeric materials have been increasingly used in various multi-layer laminates for both containers and covers. It is well known to utilize certain polymeric materials in a laminate container and cover assembly, and to thermally bond such materials together in order to initially seal the resulting package. An example of this approach is described in U.S. Pat. No. 5,062,569 for a heat sealable container and lid assembly.
If however, a resealable function is desired, it is generally not possible to effectively and reliably perform the resealing using the same polymeric materials as used for the initial thermal sealing of the container. As a result, artisans devised multi-layer laminate assemblies containing both heat sealing materials and pressure sensitive adhesives. An example of such an assembly is described in U.S. Pat. No. 3,454,210. In that patent, multilayer laminates are used in both a cover and a base assembly. A heat sealable layer between the cover and base thermally bonds the components together in an initial sealing operation. Upon removal of the cover, a layer of the cover then ruptures, thereby exposing the pressure sensitive adhesive. The lid can be resealed to the container by contacting the pressure sensitive adhesive to a corresponding face on the container. A similar strategy is also described in U.S. Pat. No. 7,422,782.
Although satisfactory in many respects, package assemblies such as that disclosed in the '210 patent have several limitations. One such limitation stems from the provision of the heat sealing material and the pressure sensitive adhesive being positioned generally within the same layer or stratum of the cover laminate. This requires careful application of heat to only those regions at which the heat sealing material exists, use of heat-resistant pressure sensitive adhesives, and careful manufacturing of the lid laminate, for example. All of these concerns increase manufacturing and sealing complexity and costs. Furthermore, potential exposure to the pressure sensitive adhesive by the contents of the container, would likely be undesirable for food packaging applications.
As a result of these and other practices in the industry, resealable lid or cover laminates utilizing an underside with a heat sealing layer, and a pressure sensitive adhesive layer disposed at a different position in the laminate have been devised. Examples of these types of resealable packaging assemblies are disclosed in U.S. Pat. No. 6,302,290; US Publication 2004/0180118; and GB 2,319,746. The '290 patent and the '118 publication are directed to resealable container assemblies with multilayer covering sheets or films that are initially heat sealed to a container, and then upon opening of the container by removal of a portion of the sheet, a bead remains thermally bonded to an upwardly facing surface of the container. The bead assists in subsequent sealing by contacting an exposed region of a pressure sensitive adhesive carried by the sheet. The bead and/or its formation is achieved by use of a shifted strata arrangement of layers in the multilayer sheet. Although satisfactory in numerous regards, these container assemblies would likely not be suitable for sensitive and perishable food items that are frequently initially vacuum sealed and/or which must exhibit low oxygen permeability properties.
As far as is known, the previously noted GB '746 patent is the earliest disclosure of a resealable lid and container assembly in which the lid and container utilize opposing heat sealing layers for initial thermal sealing of the container, the lid utilizes a multi-layer assembly with an adhesive layer that is ruptured upon opening of the sealed container, and which lid also includes a barrier layer such as formed from polyvinylidene chloride (PVDC), thereby rendering the container potentially eligible for packaging perishable and/or sensitive food items.
However, it is believed that a variety of additional limitations are associated with each of the container systems described in the previously noted '290 patent, '118 publication, and the GB '746 patent. For example, the shifted strata arrangement of layers in the covering sheets and films described in the '290 patent and the '118 publication would be tedious and costly to produce, particularly in a high volume manufacturing context. The GB '746 patent fails to disclose a practical embodiment beyond its conceptual disclosure.
As a result of these and other concerns in the industry, efforts continued in an attempt to devise a practical and commercially feasible resealable container that was particularly adapted for packaging of sensitive and/or perishable items. U.S. Pat. No. 6,056,141 describes a reclosable packing system that remedies many of the previously noted shortcomings of other resealable container and lid assemblies. The '141 patent is directed to flexible multilayer lid sheets that are initially thermally bonded to a corresponding tray or container, can be opened by removing a portion of the multilayer lid sheet to thereby expose a region of pressure sensitive adhesive carried in the sheet, and which also utilize a barrier film in the multilayer lid sheet to improve sealing characteristics of the container.
Although providing an advance in the art, the reclosable packing system of the '141 patent is relatively complex, providing up to ten (10) layers in the lid sheet assembly and up to five (5) layers in the corresponding tray assembly. It is likely that such complex assemblies would be difficult and costly to manufacture. Furthermore, the use of such a large number of layers in a multilayer lid sheet, increases the susceptibility of malfunction of the lid sheet upon initial opening by a consumer. Tearing or rupturing of the lid sheet at any location other than the intended location along the layer of the pressure sensitive adhesive, would render the lid useless and thereby destroy the reclosing function of the assembly. Accordingly, a need remains in the packaging and container arts for a resealable assembly having excellent barrier properties, and a relatively simple construction for ease in manufacturing and reliability.
In packaging food items, a disadvantage typically associated with securely sealed containers, and most notably those with high barrier characteristics, is the difficulty in initially opening the container. Even with purportedly resealable containers such as used in packaging lunchmeat and other sensitive items, it is often very difficult to open the container. If a consumer is unable to readily open or “peel” the lid or sheet away from the container, resort to scissors or other utensils is made, again, resulting in destruction of the resealing feature. Accordingly, a need remains in the art for a resealable container assembly with high barrier properties, and which is relatively simple in construction and manufacture, and which can be easily opened by a consumer.